1. Field of the Invention
The present invention relates to a system for the treatment of industrial effluent fluids such as effluent gases produced in semiconductor manufacturing, photovoltaic processing, etc. Such system may variously include an oxidizer, gas scrubbing, particulate solids removal, and other unit operations for effluent gas treatment.
2. Description of the Related Art
In the treatment of industrial fluid waste streams, a wide variety of unit operations and corresponding discrete treatment apparatus have been integrated for processing of the effluent from an upstream process facility.
For example, various integrated thermal systems are commercially available for treatment of semiconductor manufacturing effluents and photovoltaic processing off-gases. These integrated systems are typically targeted for use with CVD, metal etch, etch and ion implant tools. Commercial integrated systems include the Delatech Controlled Decomposition Oxidizer (CDO), the Dunnschicht Anlagen Systeme (DAS) Escape system, and the Edwards Thermal Processing Unit (TPU). Each of these commercially available systems consists of an integration of a thermal processing unit for oxidative decomposition of effluent gases, combined with a wet quench for temperature control of the off-gases from the hot oxidation section, and a wet scrubbing system for the removal of acid gases and particulates formed in the oxidation process.
In the Delatech CDO, the thermal system comprises an electrically heated tube, which may optionally be combined with a flame-based insertable Hydrogen Injection System (HIS) for the destruction of particularly difficult-to-remove compounds from the effluent gas stream. In the aforementioned DAS Escape system, the thermal oxidizer is flame-based, using O.sub.2 as the oxidizer and methane or hydrogen as the fuel. In the TPU, the thermal oxidizer comprises a flame-based surface combustion unit which uses air or O.sub.2 as oxidizer and methane as a fuel.
In addition to these integrated commercial systems, there are also various commercially available stand-alone single unit operational systems for the treatment of effluent gas streams, including: a) unheated physisorptive packed bed dry scrubbers, b) unheated chemisorptive packed bed dry scrubbers, c) heated chemically reacting packed bed dry scrubbers, d) heated catalytically reacting packed bed dry scrubbers, e) wet scrubbers, and f) flame-based thermal treatment units. Each of these unit operation technologies is appropriate for certain applications, depending on the nature of the gas stream undergoing treatment.
In general, each of these respective technologies is based on a distinct set of removal mechanisms for specific effluent stream constituents. These technologies can provide excellent abatement when either: a) the effluent stream constituents requiring removal are sufficiently similar in removal mechanism pathway that a single removal technology can eliminate the gases of concern, or b) when the particular subset of gas stream constituent species that is not responsive to that particular removal mechanism is of such character that the gas stream constituent species can be vented without abatement.
On occasion, the end user of the aforementioned stand-alone single unit operationally-based systems may choose to combine two or more of these various treatment units in order to provide a processing sequence for each of the categories of the various gases being passed through the system. Nonetheless, the execution of such a consolidated equipment approach is clearly less convenient for the end user than for the original equipment manufacturer, since the original equipment manufacturer can provide an integration of the various operational treatment units in a single small-sized treatment system in the first instance. The end user, by contrast, must substantially modify the component stand-alone units for consolidated assembly and operation.
Additionally, while these original equipment manufacturer-integrated effluent gas stream treatment systems clearly can, in certain applications, have advantages over single unit operational systems, typically, these integrated systems, which may for example carry out unit operations of oxidation, quenching, and scrubbing, suffer from various deficiencies, including: particulates clogging in the respective sections as well as the inlet region of the oxidizer section, generation of particulates in the oxidation section, poor scrubbing of acid gases in the scrubber section, high consumption of water for acid gas and particulate scrubbing, and condensation of saturated off-gases from the scrubber section resulting in collection and concentration of aqueous mixtures with acids.
Inlet clogging can arise from several sources including: (a) back-migration of water vapor as combustion products of the oxidizer section, causing hydrolysis reactions in a heterogeneous or homogeneous fashion with incoming water-sensitive gases such as BCl.sub.3 or WF.sub.6 ; (b) thermal degradation of incoming thermally-sensitive gases; and (c) condensation of incoming gases due to transition points in the system. These inlet clogging problems may require the incorporation of plunger mechanisms or other solids removal means to keep the inlet free of solids accumulations, however these mechanical fixes add considerable expense and labor to the system. In other instances, the inlet clogging problems may be systemic and require periodic preventative maintenance to keep the inlet free of solids accumulations. Such maintenance, however, requires shut-down of the system and loss of productivity in the manufacturing facility.
The existing integrated point of use gas effluent treatment systems may also experience problems in plant facilities which have difficulty in treating the wastewater from their wet scrubbing processes. A number of plants may have difficulties processing the fluorine (F.sup.-) species in the wastewater generated from these point of use systems, or more generally, in processing wastewater deriving from the gas effluent treatment system per se.
The water scrubber and quench portions of the integrated system can also have problems with clogging when quality of the feed water available to the process facility is poor, a typical condition in the Southwest United States. Lack of readily available water, high water costs, and high disposal costs for discharged wastewater are also significant problems in many localities. In some cases, these factors necessitate the use of high quality deionized water in the process facility to prevent clogging problems. While effective in preventing the scrubber and quench plugging, such solution involves a very high cost of ownership associated with the substantial costs of high quality deionized water.
In the scrubbing operation, poor scrubbing of acid gases in scrubber towers can be due to the small flowrates that are processed through these systems. The diameters of scrubber towers processing such small flowrates are correspondingly small, which when combined with the use of conventional large diameter packing can result in a packing element diameter to column diameter which is excessively high and results in large wall effects in the scrubber tower. Such scrubber towers as a result require large water flows, which in turn can cause channeling, flooding and slugging, with pockets of process gas passing untreated through the scrubber system. Due to the poor scrubbing of these systems, corrosion in the ducting downstream of these systems is commonly observed, which is due to condensation of the untreated off-gases from the scrubber. When halide gases are being treated in the effluent stream, the off-gases from the scrubber tower will as a result of the poor scrubbing performance of the scrubber contain unscrubbed halogen content. The unscrubbed halogen content may result in formation of pools of highly concentrated acids condensed at the volatile liquid evaporation (VLE) dewpoint condition, and a substantially higher than expected acid/water mix.
It is an object of the invention to provide an improved system for the treatment of industrial effluent gases.
It is an object of the present invention to provide an improved integrated effluent processing system, utilizing water scrubbing and oxidation treatment of the effluent gas stream.
It is a further object of the invention to provide an improved system for the treatment of industrial effluent gases, which reduces the susceptibility to clogging and solids accumulations in the system.
It is a still further object of the invention to provide an effluent gas treatment system utilizing water scrubbing, which substantially reduces the water required in the scrubbing operation, relative to scrubber systems of the prior art.
It is another object of the invention to provide such a system for the treatment of effluent gases such as are produced in the manufacture of semiconductors, photovoltaic processing, and the like, which overcome the above-discussed deficiencies of the prior art systems.
Other objects and advantages will be more fully apparent from the ensuing disclosure.